DESCRIPTION: This application is investigating the function of the ovarian tumor group genes in Drosophila oogenesis. The long-term objective is to elucidate the pathways controlling female germline differentiation. Mutants of the ovarian tumor (otu) gene display allele specific defects ranging from agametic ovaries to neoplastic growth, the least severe being incomplete maturation of the oocytes. Otu gene expression is required only in the germline. Alternative splicing of Otu transcripts results in two isoforms of 98 and 104 kd, differing by 42- aa. Rescue experiments with the 98 kd isoform causes otu mutant agametic ovaries to develop tumorous egg chambers suggesting that proliferation is normal but differentiation of the female germline is abnormal. In addition, an otu mutation which blocks the alternative splicing pathway yields only the 98kd isoform, and this mutant also has the tumorous egg chamber phenotype.